Question

The atomic and ionic radii (M${}^{3+}$ ions) of Lanthanide elements decrease with increase in atomic number. This effect is called:

• A. Lanthanoid contraction
• B. f-f transition
• C. Actinoid contraction
• D. shielding effect

Answer 1

The correct option is A Lanthanoid contraction

The greater-than-expected decrease in ionic radii of the elements in the lanthanide series is called lanthanoid contraction. The effect results from poor shielding of nuclear charge (nuclear attractive force on electrons) by 4f electrons; the 6s electrons are drawn towards the nucleus, thus resulting in a smaller atomic radius.